Techniques for implementing security on a small footprint device using a context barrier

ABSTRACT

A small footprint device, such as a smart card, can securely run multiple programs from unrelated vendors by the inclusion of a context barrier isolating the execution of the programs. The context barrier performs security checks to see that principal and object are within the same namespace or memory space and to see that a requested action is appropriate for an object to be operated upon.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.08/839,621 filed Apr. 15, 1997, entitled “VIRTUAL MACHINE WITH SECURELYDISTRIBUTED BYTE CODE VERIFICATION”, in the name of inventors Moshe Levyand Judy Schwabe (Docket No. 50253-221/P3263), which application isincorporated herein by reference in its entirety.

This application is related to U.S. patent application Ser. No. ______filed Jan. 22, 1999, entitled “TECHNIQUES FOR PERMITTING ACCESS ACROSS ACONTEXT BARRIER ON A SMALL FOOTPRINT DEVICE USING AN ENTRY POINTOBJECT”, in the name of inventors Joshua Susser, Mitchel B. Butler, andAndy Streich, (Docket No. 50253-217/P3709), which application isincorporated herein by reference in its entirety.

This application is related to U.S. patent application Ser. No. ______filed Jan. 22, 1999, entitled “TECHNIQUES FOR PERMITTING ACCESS ACROSS ACONTEXT BARRIER ON A SMALL FOOTPRINT DEVICE USING RUN TIME ENVIRONMENTPRIVILEGES”, in the name of inventors Joshua Susser, Mitchel B. Butler,and Andy Streich, (Docket No. 50253-218/P3710), which application isincorporated herein by reference in its entirety.

This application is related to U.S. patent application Ser. No. ______filed Jan. 22, 1999, entitled “TECHNIQUES FOR PERMITTING ACCESS ACROSS ACONTEXT BARRIER IN A SMALL FOOTPRINT DEVICE USING GLOBAL DATASTRUCTURES”, in the name of inventors Joshua Susser, Mitchel B. Butler,and Andy Streich, (Docket No. 50253-219/P3711), which application isincorporated herein by reference in its entirety.

This application is related to U.S. patent application Ser. No. ______filed Jan. 22, 1999, entitled “TECHNIQUES FOR PERMITTING ACCESS ACROSS ACONTEXT BARRIER IN A SMALL FOOTPRINT USING SHARED OBJECT INTERFACES”, inthe name of inventors Joshua Susser, Mitchel B. Butler, and AndyStreich, (Docket No. 50253-220/P3712), which application is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to computer security and more particularly totechniques for implementing a security on small footprint devices, suchas smart cards.

2. Description of Related Art

A number of object oriented programming languages are well known in theart. Examples of these include the C++ language and the Smalltalklanguage.

Another such object oriented language is the JAVA™ language. Thislanguage is described in the book Java™ Language Specification, by JamesGosling et al. and published by Addison-Wesley. This work isincorporated herein by reference in its entirety. The JAVA™ language isparticularly well suited to run on a Java™ Virtual Machine. Such amachine is described in the book Java™ Virtual Machine Specification, byTim Lindholm and Frank Yellin which is also published by Addison-Wesleyand which is also incorporated herein by reference in its entirety.

A number of small footprint devices are also well known in the art.These include smart cards, cellular telephones, and various other smallor miniature devices.

Smart cards are similar in size and shape to a credit card but contain,typically, data processing capabilities within the card (e.g. aprocessor or logic performing processing functions) and a set ofcontacts through which programs, data and other communications with thesmart card may be achieved. Typically, the set of contacts includes apower source connection and a return as well as a clock input, a resetinput and a data port through which data communications can be achieved.

Information can be written to a smart card and retrieved from a smartcard using a card acceptance device. A card acceptance device istypically a peripheral attached to a host computer and contains a cardport, such as a slot, in to which a smart card can be inserted. Onceinserted, contacts or brushes from a connector press against the surfaceconnection area on the smart card to provide power and to permitcommunications with the processor and memory typically found on a smartcard.

Smart cards and card acceptance devices (CADs) are the subject ofextensive standardization efforts, e.g. ISO 7816.

The use of firewalls to separate authorized from unauthorized users iswell known in the network environment. For example, such a firewall isdisclosed in U.S. patent application Ser. No. 09/203,719, filed Dec. 1,1998 and entitled “AUTHENTICATED FIREWALL TUNNELLING FRAMEWORK” in thename of inventor David Brownell (Docket No. 50435-023/P2789/TJC), whichapplication is incorporated herein by reference in its entirety.

A subset of the full Java™ platform capabilities has been defined forsmall footprint devices, such as smart cards. This subset is called theJava Card™ platform. The uses of the Java Card™ platform are describedin the following publications.

-   -   JAVA CARD™ 2.0—LANGUAGE SUBSET AND VIRTUAL MACHINE        SPECIFICATION;    -   JAVA CARD™ 2.1—APPLICATION PROGRAMMING INTERFACES;    -   JAVA CARD™ 2.0—PROGRAMMING CONCEPTS;    -   JAVA CARD™ APPLET DEVELOPER'S GUIDE.

These publications are incorporated herein by reference in theirentirety.

A working draft of ISO 7816—Part 11 has been circulated for comment.That draft specifies standards for permitting separate executioncontexts to operate on a smart card. A copy of that working draft ishereby incorporated by reference in its entirety.

The notion of an execution context is well known in computer science.Generally speaking, the use of multiple execution contexts in acomputing environment provides a way to separate or isolate differentprogram modules or processes from one another, so that each can operatewithout undue interference from the others. Interactions—if any—betweendifferent contexts are deliberate rather than accidental, and arecarefully controlled so as to preserve the integrity of each context. Anexample of multiple contexts is seen in larger hardware devices, such asmainframes, where a plurality of virtual machines may be defined, eachsuch virtual machine having its own execution context. Another exampleis seen in U.S. Pat. No. 5,802,519 in the name of inventor De Jong,which describes the use of multiple execution contexts on a smart card.It will be appreciated by those of skill in the art that a computingenvironment which provides multiple execution contexts also needs toprovide a mechanism for associating any given executing code with itscorresponding context.

Also well known is the notion of a current context. Certain computingenvironments that support multiple contexts will, at any given time,treat one context in particular as an active focus of computation. Thecontext can be referred to as the “current context.” When the currentcontext changes, so that some other context becomes the current context,a “context switch” is said to occur. As will be appreciated by those ofskill in the art, these computing environments provide mechanisms forkeeping track of which context is the current one and for facilitatingcontext switching.

In the prior art, in the world of small footprint devices, andparticularly in the world of smart cards, there was no inter-operationbetween contexts operating on the small footprint devices. Each contextoperated totally separately and could operate or malfunction within itscontext space without affecting other applications or processes in adifferent context.

One layer of security protection utilized by the Java™ platform iscommonly referred to as a sandbox model. Untrusted code is placed into a“sandbox” where it can “play” safely without doing any damage to the“real world” or full Java™ environment. In such an environment, Java™applets don't communicate, but each has its own name space.

Some smart card operating systems don't permit execution contexts tocommunicate directly, but do permit communications through an operatingsystem, or through a server.

The Problems

A number of problems exist when trying to place computer programs andother information on a small footprint device. One of the compellingproblems is the existence of very limited memory space. This requiresoften extraordinary efforts to provide needed functionality within thememory space.

A second problem associated with small footprint devices is the factthat different small footprint device manufacturers can utilizedifferent operating systems. As a result, applications developed for oneoperating system are not necessarily portable to small footprint devicesmanufactured by a different manufacturer.

If programs from more than one source of programs (manufacturer orvendor) are to be applied to a single small footprint device, securitybecomes a factor as one attempts to avoid corruption of existingprograms and data when a new program is loaded on to the small footprintdevice. The same concern exists when one wishes to prevent a hacker or amalicious person from accessing programs and data.

It is clear that small footprint devices such as smart cards don't havethe resources necessary to implement separate virtual machines.Nevertheless, it is desirable to maintain strict security betweenseparate execution contexts.

In the past, security was provided by loading only applications from thesame source or from a known trusted source onto a smart card or othersmall footprint device.

Accordingly, it would be desirable to allow object-oriented interactionbetween selected execution contexts only in safe ways via fast efficientpeer to peer communications which do not impose undue burdens on theprogrammer but facilitate dynamic loading of applets written atdifferent times by untrusted sources.

SUMMARY OF THE INVENTION

The invention is directed to providing a context barrier (sometimesreferred to as a firewall) for providing separation and isolation of onecontext from another and to provide controlled access across the barrierwhen that is needed.

In accordance with the invention, two execution contexts, e.g. eachcontaining one or more applets, running in the same logical (i.e.,virtual or real) machine, protected from each other, can shareinformation in a controlled, secure way, using language mechanisms, suchas object-oriented language mechanisms. Security can be, for example,object by object. Thus, a method in a first execution context can accessa first object A in a second execution context, but not a second objectB in the second execution context on a selective basis.

In accordance with one exemplary embodiment, an enhanced Java™ VirtualMachine (VM) provides certain run-time checks of attempted access acrossexecution contexts in the VM. Checks can be automatic by the VM or codedby the programmer with support from the VM. This can be done usinglanguage-level communication mechanisms. In this way, one can expressobject access across execution contexts in the same way as other objectaccesses using the language are made. These run-time checks provide asecond dimension of defense/security beyond that which the Java™language and platform already provide.

These mechanisms provide protection against, e.g., security holes due toprogramming bugs (such as declaring a datum “public” (global) when itshouldn't be accessible to all contexts). They also allow fine-graincontrol of sharing (such as selection of objects to share and applets toshare to).

The invention is also directed to computer program products and carrierwaves related to the other aspects of the invention.

The foregoing and other features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be apparentfrom the following description in which:

FIG. 1 is an illustration of a computer equipped with a card acceptancedevice and of a smart card for use with the card acceptance device.

FIG. 2 is an illustration of a computer equipped with a card acceptancedevice connected to a network.

FIG. 3 is an exemplary hardware architecture of a small footprintdevice, such as a smart card, of the prior art.

FIG. 4 illustrates objects being accessed by principals as done in theprior art.

FIG. 5 is an exemplary security model which can be used in explainingthe various embodiments of the invention.

FIG. 6 is a block diagram showing separation of execution contexts by afirewall or context barrier in accordance with one aspect of theinvention.

FIG. 7 is a representation of a software architecture useful in carryingout the invention.

FIG. 8 is a flow chart of a security enforcement process implementing afirewall in accordance with one aspect of the invention.

FIG. 9 is a block diagram showing object access across a firewall inaccordance with one aspect of the invention.

FIG. 10 is a block diagram showing cascaded object access across afirewall.

FIG. 11 is a flow chart of a process for permitting access by aprincipal in one context across a firewall into another context.

FIG. 12 is a block diagram illustrating the use of an entry point objectto permit access across a firewall.

FIG. 13 is a block diagram illustrating the use of a global datastructure such as an array for access across a firewall.

FIG. 14 is a block diagram illustrating the use of a supercontext topermit access across a firewall.

FIG. 15 is a block diagram illustrating the use of shareable interfaceobjects to permit access across a firewall.

FIG. 16 is a flow chart of a security enforcement process permittingaccess across a firewall.

FIG. 17 is the flow chart of FIG. 16 showing details of block 1620.

FIG. 18 is a flow chart showing an exemplary implementation of block1629 of FIG. 17.

NOTATIONS AND NOMENCLATURE

The detailed descriptions which follow may be presented in terms ofprogram procedures executed on a computer or network of computers. Theseprocedural descriptions and representations are the means used by thoseskilled in the art to most effectively convey the substance of theirwork to others skilled in the art.

A procedure is here, and generally, conceived to be a self-consistentsequence of steps leading to a desired result. These steps are thoserequiring physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. It proves convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers, or thelike. It should be noted, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities.

Further, the manipulations performed are often referred to in terms,such as adding or comparing, which are commonly associated with mentaloperations performed by a human operator. No such capability of a humanoperator is necessary, or desirable in most cases, in any of theoperations described herein which form part of the present invention;the operations are machine operations. Useful machines for performingthe operation of the present invention include general purpose digitalcomputers or other computational devices.

The present invention also relates to apparatus for performing theseoperations. This apparatus may be specially constructed for the requiredpurpose or it may comprise a general purpose computer as selectivelyactivated or reconfigured by a computer program stored in the computer.The procedures presented herein are not inherently related to aparticular computer or other apparatus. Various general purpose machinesmay be used with programs written in accordance with the teachingsherein, or it may prove more convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these machines will appear from the description given.

DETAILED DESCRIPTION

Attached as an Appendix to this specification is an unpublished draft ofa document entitled JAVA CARD RUNTIME ENVIRONMENT 2.1 SPECIFICATION.This draft document, which provides further detailed description ofspecific embodiments of the invention, is incorporated in its entiretyas an integral part of the present specification.

Although the inventive techniques are described hereinafter in thecontext of a smart card example, the example is merely illustrative andshouldn't limit the scope of the invention.

FIG. 1 is an illustration of a computer 120 equipped with a cardacceptance device 110 and a smart card 100 for use with the cardacceptance device 110. In operation, the smart card 100 is inserted intocard acceptance device 110 and power and data connections appliedthrough a set of contacts 105 accessible at the surface of the smartcard 100. When the card is inserted, mating contacts from the cardacceptance device 110 interconnect with the surface contacts 105 topower-up the card and permit communications with the onboard processorand memory storage.

FIG. 2 is an illustration of a computer equipped with a card acceptancedevice, such as 120 in FIG. 1, connected to a network 200. Alsoconnected to a network are a plurality of other computing devices, suchas server 210. It is possible to load data and software onto a smartcard over the network 200 using card equipped device 120. Downloads ofthis nature can include applets or other programs to be loaded onto asmart card as well as digital cash and other information used inaccordance with a variety of electronic commerce and other applications.The instructions and data used to control processing elements of thecard acceptance device and of the smart card may be stored in volatileor non-volatile memory or may be received directly over a communicationslink, e.g., as a carrier wave containing the instructions and/or data.Further, for example, the network can be a LAN or a WAN such as theInternet or other network.

FIG. 3 is an exemplary hardware architecture of a small footprintdevice, such as a smart card, of the prior art. As shown in FIG. 3, aprocessor 300 interconnects with primary storage 310 which may includeread only memory 315 and/or random access memory 316. The processor alsoconnects with a secondary storage 320 such as EEPROM and with aninput/output 330, such as a serial port. One can see the small footprintdevices of this nature can be very simple.

FIG. 4 illustrates objects being accessed by principals as done in theprior art. As shown in FIG. 4, physical device 400, such as the smallfootprint device may have contained within it one or more processingmachines (virtual or physical) which are running an execution context420. The execution context may be, for example, a context associatedwith a particular applet. One or more principals 430 (e.g., applets orapplications) in the execution context may seek to access other objectswithin the execution context. As long as the access occurs within theexecution context, the accesses will be permitted and everything willfunction normally.

FIG. 5 is an exemplary security model which can be used in explainingthe various embodiments of the invention. It is just one of many modelswhich might be utilized but is a convenient model for this purpose. Inthis model, a principal (sometimes called entity) 500 proposes to takean action 510 on an object, such as object 520. Security checks may beimposed on the principal, on the object, and/or on the action proposedto be taken.

In FIG. 5, two types of objects are shown on which action may be takenby a principal. These include data objects, (e.g. data1 and data2 (520,520′)) and entity 530. A principal may operate or attempt to operate onany of these objects.

While data is passive, an entity 530 is active. The diagram line fromPrincipal to an active entity is also labeled “action,” but this couldbe a more sophisticated and arbitrarily complex action, such as making afunction or method call or sending a message as compared with action ona data object. As with data, a security check enforced by the operatingsystem may use the identity of the principal, the identity of theentity, and/or the type of action. Furthermore, the entity, beingactive, can perform its own additional security checks. These can be asarbitrarily complex as one desires, and can make use of the identity ofthe Principal, the identity of the entity itself, the action, and/or anyother information that is available.

In an object-oriented system (such as the Java Card™ platform) “objects”are typically a combination of data and entity. When a Principal triesto access a field of an object, this is a data access—a fairly simpleaction protected by a fairly simple security check. When a Principaltries to access a method of an object, this is an entity access, whichcan be arbitrarily complex both in action and in security check.

FIG. 6 is a block diagram showing separation of execution contexts by afirewall or context barrier in accordance with one aspect of theinvention. The physical device 400 and the machine 410 correspond to thesame items shown in FIG. 4. An execution context 420 shows one principal430 attempting to access object 440 within the context. This accesswould normally succeed. However, execution context 420 also shows aprincipal 630 attempting to access object 640 of execution context 620,across a context barrier 600. Normally, this access would be prohibitedas indicated by the X 636 where the action 635 crosses the contextbarrier 600.

FIG. 7 is a representation of a software architecture useful in carryingout the invention. This software architecture is shown as a run timeenvironment 700. An operating system 710 for the small footprint deviceis commonly used. A virtual machine 720, in an exemplary embodiment ofthe invention, is implemented over the operating system. The virtualmachine could be a Java Card™ virtual machine or other virtual machine.The capabilities of a standard virtual machine can be expanded toprovide the additional functionality described herein or thefunctionality can be provided as separate modules. The virtual machine720 may include an interpreter or native implementation 730 whichprovides access to a run time system 740. The run time system includesobject system 750 for managing the objects of an object orientedimplementation. Three contexts, 760, 770 and 780, are shown. Eachcontext is separated from the other by a context barrier (sometimesreferred to as a firewall) between the execution contexts. Context 760is, in one specific embodiment, a supercontext. That is, context 760 hasprivileges and capabilities not available to subordinate contexts 770and 780, potentially including privileges to create entry point objectsor global data structures, and to access objects in subordinate contexts770 and 780.

Every object is associated with one particular context. That context issaid to own each object that is associated with it. The runtime system740 provides a means for uniquely identifying contexts, and a means forspecifying and identifying the currently executing context. The objectsystem 750 provides a mechanism for associating objects with theirowning contexts.

For example, the runtime 740 can identify contexts with a unique name,and correspondingly the object system 750 can associate objects withthat context by recording the context's name in the object's header.Information in the object's header cannot be accessed by programswritten in the object-oriented language, but is only available to thevirtual machine 720 itself. Alternately, the runtime system 740 canidentify contexts by dividing the memory space into separate regions,each for a particular context, and correspondingly the object system 750can associate objects with that context by allocating the object'sstorage in that context's memory space.

FIG. 8 is a flow chart of a security enforcement process implementing acontext barrier in accordance with one aspect of the invention. When aprincipal invokes an action on an object (800) a check is made todetermine whether the object is within the context of the principal(810). If it is not, the action is disallowed (840). Otherwise, theaction is permitted (830). This is the simplest form of context barrieror firewall. In one specific embodiment the action is disallowed (840)by throwing a security exception if the object is outside of thenamespace or the memory space of the context requesting access.

FIG. 9 is a block diagram showing object access across a firewall inaccordance with one aspect of the invention. FIG. 9 is substantiallysimilar to FIG. 6. However, FIG. 9 also shows principal 900 seeking toaccess object 910 in order to perform action 905 on the object 910.According to the invention, rather than having the access blocked by thefirewall 600, in the way that action 635 is blocked, action 905 ispermitted to occur across the firewall through access point 920 so thatprincipal 900 can perform action 905 on object 910 notwithstanding thefact that the principal and the object are in different executioncontexts. The mechanisms behind access point 920 are described belowwith reference to FIGS. 12-18. Note that access point 920 can coexistwith obstructed accesses such as X 636. Thus access point 920 providesfine-grain control of sharing (object by object security) across contextbarrier 600.

When object access 900 is initiated, the current context setting iscontext 420. If the object 910 is a data object, the action 905 is asimple data access, and no code is executed in the second context 620.If the object 910 is an entity object, and the action 905 results inthat object's code being executed, that code is executed in the secondcontext 620. To execute the code of object 910 in the correct context620, the virtual machine 410 performs a context switch. The contextswitch changes the current context setting to be context 620, and theprevious value of the current context setting is stored so that it canbe restored later. From that point on code will execute in the newcurrent context. When the action 905 completes, control is returned tothe point following access 900. During the return, the virtual machine410 must restore the value of the current context setting to itsprevious value.

FIG. 10 is a block diagram showing cascaded object accesses across afirewall. FIG. 10 shows three execution contexts, 1000, 1010 and 1020.Principal 1030 in execution context 1 seeks to invoke an action 1035 onobject 1050 in execution context 2 and does so through access point 1070in context barrier 600. Object 1050 in execution context 2 has an objectaccess 1040 which seeks to perform an action 1045 on the object 1060 inexecution context 3. It achieves this by using access point 1080 incontext barrier 600′ separating execution contexts 2 and 3. Object 1050in execution context 2 also has another object access 1090 which invokesan action 1095 on an object 1099 in the same execution context, that is,in execution context 2. Both actions 1035 and 1045 result in contextswitches as described in the explanation of FIG. 9. But as action 1095does not cross the context barrier, a context switch is not required forits execution, and therefore does not occur.

FIG. 11 is a flow chart of a process for permitting access by aprincipal in one context across a firewall into another context. Thereare essentially three steps to this process. In execution context 2, anobject to be accessed is created and designated as shared (1100). Inexecution context 1, the principal obtains a reference to the object inexecution context 2 (1110). The principal in execution context 1 theninvokes an action upon the object designated as shared in context 2(1120).

With respect to identifying or designating a created object as shareableas discussed in item 1100 of FIG. 11, this can be done, in accordancewith a specific embodiment of the invention, by including a shareableattribute in the header of an object's representation. Information in anobject's header cannot be accessed by programs written in theobject-oriented language, but is only available to the VM itself.

Obtaining a reference to an object in another context is a special caseof accessing an object in another context. A mechanism that providesaccess to an object in another context can make other objects availablealso. For instance, invoking a method on an object in another contextmay return a reference to a second object in a different context. Anadditional mechanism is required to allow an initial reference to anobject in a different context to be obtained. In a specific embodiment,references to certain well-known entry point objects can be obtainedusing a public API. Once the initial reference to an object in adifferent context is obtained, further references can be obtained fromthat object, and so on.

There are four general approaches to obtaining information across acontext barrier in accordance with the invention. These approaches canbe utilized individually or in combination in order to access an objectacross a context barrier or to obtain a reference of an object to beaccessed across a context barrier (1110). These approaches are describedin FIGS. 12-18.

FIG. 12 is a block diagram illustrating the use of entry point objectsto permit access across a context barrier. As shown in FIG. 12, someobject 1200 in context 770 (context 1) desires access to information insupercontext 760. In the specific embodiment, a supercontext 760contains at least one entry point object 1210. The entry point object1210 can be published as part of a public API, or can be made availableindirectly through a published API (e.g., in accordance with themechanisms described previously with reference to FIG. 11), so that eachcontext subordinate to the supercontext may communicate with the entrypoint object of the supercontext. (It will be appreciated that in otherembodiments, entry point objects may be housed by a context other thanthe supercontext.)

FIG. 13 is a block diagram illustrating the use of global datastructures to permit access across a firewall. In this approach,supercontext 760 creates a global data structure such as a global array.In the specific embodiment supercontext 760 is the only contextpermitted to create such a global data structure. (It will beappreciated that in other embodiments, global data may be housed by acontext other than the supercontext.) By virtue of its global status,each of the contexts 770 and 780 may read and write to the global datastructure. Thus, information written into the global data structure byone context can be read by another context. For example, this mechanismcan be used to pass binary data or references to objects betweencontexts.

FIG. 14 is a block diagram illustrating the use of supercontextprivileges to permit access across a context barrier. In FIG. 14, anobject in supercontext 760 seeks access to context 780 across thecontext barrier separating the two. Supercontext 760 can invoke any ofthe methods of context 780 and can access any of the data containedwithin context 780, by virtue of the privileges associated with thesupercontext.

FIG. 15 is a block diagram illustrating the use of shareable interfaceobjects to permit access across a firewall. A shareable interfacedefines a set of shareable interface methods. A shareable interfaceobject is an object that implements at least the set of methods definedin a shareable interface. In FIG. 15, object 1210 in context 2 (780) isa shareable interface object. An object access 1200 in another context770 can invoke any of the shareable interface methods on the object 1210if the principal of the object access 1200 is authorized to do so by theobject 1210 itself. This authorization is further discussed withreference to FIG. 18 below.

It will be appreciated that a virtual machine consistent with theinvention provides functionality beyond that of earlier virtualmachines, such as the virtual machine described in the Java™ VirtualMachine Specification. In particular, consistently with the invention,the virtual machine provides functionality to implement or to facilitatea security enforcement process that permits access across a firewall.This process is described next with reference to FIGS. 16-18. Note thatit is applicable to any approach for providing access across thefirewall, including but not limited to the four approaches describedwith reference to FIGS. 12-15 above.

FIG. 16 is a flow chart of a security enforcement process permittingaccess across a firewall. When a principal attempts to invoke action onan object 1600, a check is made to determine if the object is within thecontext of the principal (1610). If it is, (1610-Y), the action ispermitted (1630). If it is not, (1610-N), a check is made to see if theaction by the principal is permitted on the object (1620). If it is,(1620-Y), the action is permitted (1630). If it is not, (1620-N), theaction is disallowed. In the specific embodiment a security exception isthrown (1640).

FIG. 17 is the flow chart of FIG. 16 showing further details of block1620. If the object is not within the context of the principal (1610-N),a plurality of tests, 1621, 1622, 1623 . . . 1629 are undertaken to seeif the action by the principal is permitted on the object. These testscan be done by the virtual machine alone or by the virtual machine plusthe object, in a virtual machine object oriented implementation. If anyof the tests results in a pass, the action is permitted (1630). However,if all tests result in a negative determination (162X—No), the actionwill be disallowed. In a specific embodiment, a security exception willbe thrown (1640). These tests relate to the permitted access discussedin conjunction with FIGS. 12-15.

FIG. 18 is a flow chart showing an exemplary implementation of block1629 of FIG. 17 for use with access method described in FIG. 15. In atest, such as 829 or 1629, a virtual machine checks if the object is ashared object 1810. If it is not (1810-No), the test will fail. However,if it is (1810-Yes), the virtual machine will invoke the method A onobject O (1820). If the method A on object O determines that theprincipal is authorized (1830), the test will be passed (1840) andaccess permitted. Otherwise, the test will fail (1850). This allows theauthorization text to be programmed into the code of the object itself.

Although the invention has been illustrated with respect to a smart cardimplementation, the invention applies to other devices with a smallfootprint, not just to smart cards. Devices with a small footprint aregenerally considered to be those that are restricted or limited inmemory or in computing power or speed. Such small footprint devices mayinclude boundary scan devices, field programmable devices, pagers andcellular phones among many others.

In general, small footprint devices are resource constrainedcomputational devices and systems where secure interoperation ofexecution contexts is a concern. Such small devices impose constraintson the implementation of security measures because of their limitedresources. Because of resource constraints, in a virtual machineimplementation, a single virtual or physical machine must be used asopposed to multiple virtual machines.

The invention may also be applied to devices with larger footprintswhere the characteristics of the invention may prove beneficial. Forexample, the invention may prove advantageous when using serylets ifthere is object sharing between them. Even some desktop systems mayprofitably utilize the techniques of the invention.

While the Java™ language and platform are suitable for the invention,any language or platform having certain characteristics would be wellsuited for implementing the invention. These characteristics includetype safety, pointer safety, object-oriented, dynamically linked, andvirtual-machine based. Not all of these characteristics need to bepresent in a particular implementation. In some embodiments, languagesor platforms lacking one or more of these characteristics may beutilized. A “virtual machine” could be implemented either in bits(virtual machine) or in silicon (real/physical machines).

Although the invention has been illustrated showing object by objectsecurity, other approaches, such as class by class security could beutilized.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims and their equivalents.

1. A small footprint device comprising: at least one processing elementconfigured to execute each group of groups of one or more programmodules in a different context, said one or more program modulescomprising zero or more sets of executable instructions and zero or moresets of data definitions, said zero or more sets of executableinstructions and said zero or more data definitions grouped as objectdefinitions; a memory comprising instances of objects; and a contextbarrier for separating and isolating said contexts wherein eachdifferent context owns at least one group of said groups associated withsaid different context and further wherein said each context comprises aprotected object instance space such that at least one of said objectdefinitions is instantiated in association with that context, saidcontext barrier configured for controlling execution of at least oneinstruction of one of said zero or more sets of executable instructionsof a program module based at least in part on whether said at least oneinstruction is executed for an object instance associated with a firstcontext and whether said at least one instruction is requesting accessto an instance of an object definition associated with a second contextdifferent from said first context, said context barrier furtherconfigured to prevent said access if said access is unauthorized andenable said access if said access is authorized. 2-24. (canceled) 25.The small footprint device of claim 1 wherein said at least oneprocessing element comprises a virtual machine running on a processor.26. The small footprint device of claim 25 further comprising a cardoperating system wherein said virtual machine runs on top of said cardoperating system.
 27. The small footprint device of claim 1 wherein saidcontext barrier allocates separate respective name spaces for eachcontext.
 28. The small footprint device of claim 1 wherein said contextbarrier allocates separate respective memory spaces for each context.29. The small footprint device of claim 1 wherein at least one programmodule comprises a plurality of applets.
 30. The small footprint deviceof claim 1 wherein said context barrier enforces at least one securitycheck on at least one of principal, object or action to prevent accessfrom a principal in one context to an object in a different context. 31.The small footprint device of claim 30 wherein said at least onesecurity check is based on partial name agreement between a principaland an object.
 32. The small footprint device of claim 30 wherein saidat least one security check is based on memory space agreement between aprincipal and an object.
 33. The small footprint device of claim 1wherein: said memory comprises object header data, said object headerdata comprising information associated with at least one of saidinstances of objects; and said controlling execution is based at leastin part on said object header data.
 34. The small footprint device ofclaim 1 wherein said memory is partitioned into a plurality of memoryspaces with instances of objects allocated for storage in one of saidplurality of memory spaces; and said controlling execution is based atleast in part on determining the memory space allocated to an executingobject instance and an accessed object instance.
 35. A method ofoperating a small footprint device that includes a processing machine,wherein program modules are executed on the processing machine, themethod comprising: executing groups of one or more program modules inseparate contexts, said one or more program modules comprising zero ormore sets of executable instructions and zero or more sets of datadefinitions, said zero or more sets of executable instructions and saidzero or more data definitions grouped as object definitions; andseparating and isolating said contexts by a context barrier wherein eachdifferent context owns at least one group of said groups associated withsaid different context and further wherein said each context comprises aprotected object instance space such that at least one of said objectdefinitions is instantiated in association with that context;controlling execution, by said context barrier, of at least oneinstruction of one of said zero or more sets of executable instructionsof a program module based at least in part on whether said at least oneinstruction is executed for an object instance associated with a firstcontext and whether said at least one instruction is requesting accessto an instance of an object definition associated with a second contextdifferent from said first context; preventing said access, by saidcontext barrier, if said access is unauthorized; and enabling saidaccess, by said context barrier if said access is authorized.
 36. Themethod of claim 35 further comprising: implementing the context barrierusing a virtual machine.
 37. The method of claim 35 further comprising:preventing, by said context barrier, a principal from accessing anobject unless both principal and object are part of the same name space.38. The method of claim 35 further comprising: preventing, by saidcontext barrier, a principal from accessing an object unless bothprincipal and object are part of the same memory space.
 39. The methodof claim 35 wherein said controlling execution is based at least in parton object header data comprising information associated with at leastone of said instances of objects.
 40. The method of claim 35 furthercomprising: partitioning a memory of said small footprint device into aplurality of memory spaces with instances of objects allocated forstorage in one of said plurality of memory spaces; and said controllingexecution is based at least in part on determining the memory spaceallocated to an executing object instance and an accessed objectinstance.
 41. The method of claim 35 further comprising: preventing, bysaid context barrier, a principal from performing an action on an objectunless both principal and object are part of the same context.
 42. Themethod of claim 41 further comprising: preventing, by said contextbarrier, a principal from performing an action on an object when saidprincipal and said action are not part of the same context if theprincipal is authorized to perform the action on the object.
 43. Themethod of claim 42 wherein the principal is authorized if the principalpasses at least one security check.
 44. The method of claim 43 whereinsaid at least one security check is one of a plurality of securitychecks.
 45. The method of claim 42 wherein, if a principal in a firstcontext is authorized to perform one or more actions on an object in asecond context, when the action is performed the action executes withinthe second context.
 46. The method of claim 45 wherein, when one or moreactions are authorized in the second context, subsequent actions areauthorized based on executing in the second context, and a principal inthe second context accesses objects in the second context.
 47. Themethod of claim 46 wherein, when one or more actions complete in thesecond context, execution returns to the first context.
 48. The methodof claim 45 wherein, when action is undertaken in the second contextthat requires access to an object in a third context, the actionexecutes within the third context.
 49. The method of claim 48 whereinswitches to a new context occur any time action is authorized on anobject in the new context.
 50. A computer program product comprising: amemory medium; and a computer controlling element comprisinginstructions for implementing a context barrier on a small footprintdevice, said small footprint device comprising: at least one processingelement configured to execute each group of groups of one or moreprogram modules in a different context, said one or more program modulescomprising zero or more sets of executable instructions and zero or moresets of data definitions, said zero or more sets of executableinstructions and said zero or more data definitions grouped as objectdefinitions; a memory comprising instances of objects; and a contextbarrier for separating and isolating said contexts wherein eachdifferent context owns at least one group of said groups associated withsaid different context and further wherein said each context comprises aprotected object instance space such that at least one of said objectdefinitions is instantiated in association with that context, saidcontext barrier configured for controlling execution of at least oneinstruction of one of said zero or more sets of executable instructionsof a program module based at least in part on whether said at least oneinstruction is executed for an object instance associated with a firstcontext and whether said at least one instruction is requesting accessto an instance of an object definition associated with a second contextdifferent from said first context, said context barrier furtherconfigured to prevent said access if said access is unauthorized andenable said access if said access is authorized.
 51. The computerprogram product of claim 50 wherein said memory medium is a carrierwave.
 52. A computer program product comprising: a memory medium; and acomputer controlling element comprising instructions for separating aplurality of programs on a small footprint device, said small footprintdevice comprising: at least one processing element configured to executeeach group of groups of one or more program modules in a differentcontext, said one or more program modules comprising zero or more setsof executable instructions and zero or more sets of data definitions,said zero or more sets of executable instructions and said zero or moredata definitions grouped as object definitions; a memory comprisinginstances of objects; and a context barrier for separating and isolatingsaid contexts wherein each different context owns at least one group ofsaid groups associated with said different context and further whereinsaid each context comprises a protected object instance space such thatat least one of said object definitions is instantiated in associationwith that context, said context barrier configured for controllingexecution of at least one instruction of one of said zero or more setsof executable instructions of a program module based at least in part onwhether said at least one instruction is executed for an object instanceassociated with a first context and whether said at least oneinstruction is requesting access to an instance of an object definitionassociated with a second context different from said first context, saidcontext barrier further configured to prevent said access if said accessis unauthorized and enable said access if said access is authorized. 53.The computer program product of claim 52 wherein said memory medium is acarrier wave.
 54. A carrier wave carrying instructions for implementinga context barrier on a small footprint device over a communicationslink, said small footprint device comprising: at least one processingelement configured to execute each group of groups of one or moreprogram modules in a different context, said one or more program modulescomprising zero or more sets of executable instructions and zero or moresets of data definitions, said zero or more sets of executableinstructions and said zero or more data definitions grouped as objectdefinitions; a memory comprising instances of objects; and a contextbarrier for separating and isolating said contexts wherein eachdifferent context owns at least one group of said groups associated withsaid different context and further wherein said each context comprises aprotected object instance space such that at least one of said objectdefinitions is instantiated in association with that context, saidcontext barrier configured for controlling execution of at least oneinstruction of one of said zero or more sets of executable instructionsof a program module based at least in part on whether said at least oneinstruction is executed for an object instance associated with a firstcontext and whether said at least one instruction is requesting accessto an instance of an object definition associated with a second contextdifferent from said first context, said context barrier furtherconfigured to prevent said access if said access is unauthorized andenable said access if said access is authorized.
 55. A carrier wavecarrying instructions over a communications link for separating aplurality of programs on a small footprint device, said small footprintdevice comprising: at least one processing element configured to executeeach group of groups of one or more program modules in a differentcontext, said one or more program modules comprising zero or more setsof executable instructions and zero or more sets of data definitions,said zero or more sets of executable instructions and said zero or moredata definitions grouped as object definitions; a memory comprisinginstances of objects; and a context barrier for separating and isolatingsaid contexts wherein each different context owns at least one group ofsaid groups associated with said different context and further whereinsaid each context comprises a protected object instance space such thatat least one of said object definitions is instantiated in associationwith that context, said context barrier configured for controllingexecution of at least one instruction of one of said zero or more setsof executable instructions of a program module based at least in part onwhether said at least one instruction is executed for an object instanceassociated with a first context and whether said at least oneinstruction is requesting access to an instance of an object definitionassociated with a second context different from said first context, saidcontext barrier further configured to prevent said access if said accessis unauthorized and enable said access if said access is authorized. 56.A method of shipping code over a network, comprising transmitting ablock of code from a server, said block of code comprising instructionsover a communications link for separating a plurality of programs on asmall footprint device, said small footprint device comprising: at leastone processing element configured to execute each group of groups of oneor more program modules in a different context, said one or more programmodules comprising zero or more sets of executable instructions and zeroor more sets of data definitions, said zero or more sets of executableinstructions and said zero or more data definitions grouped as objectdefinitions; a memory comprising instances of objects; and a contextbarrier for separating and isolating said contexts wherein eachdifferent context owns at least one group of said groups associated withsaid different context and further wherein said each context comprises aprotected object instance space such that at least one of said objectdefinitions is instantiated in association with that context, saidcontext barrier configured for controlling execution of at least oneinstruction of one of said zero or more sets of executable instructionsof a program module based at least in part on whether said at least oneinstruction is executed for an object instance associated with a firstcontext and whether said at least one instruction is requesting accessto an instance of an object definition associated with a second contextdifferent from said first context, said context barrier furtherconfigured to prevent said access if said access is unauthorized andenable said access if said access is authorized.